Al Hamra Tower: 412 m su Kuwait City
Located in Kuwait City, Al Hamra Tower anchors a commercial complex comprising offices, a health club, and a high-end shopping mall with theaters and a food court. Reaching 412 meters, the iconic office tower will be the tallest building in Kuwait.
Project Completion Year: 2011
Design Completion Year: 2006
Site Area: 10,000 m2
Project Area: 195,000 m2
Number of Stories: 74
Building Height: 412 m
2012 • Institution of Structural Engineers • Award for Commercial or Retail Structure
2012 • National Council of Structural Engineers Association • International Structures over $100 Million
2012 • Popular Science Magazine • Best of What's New
2012 • Structural Engineers Association of California • Award of Excellence: Landmark Structures
2012 • Structural Engineers Association of Northern California • Award of Excellence: Landmark Structures
2011 • Emporis • Skyscraper Award: Silver Medal
2010 • Cityscape • Commercial / Mixed Use Built
2008 • Chicago Athenaeum • International Architecture Award
2008 • Chicago Athenaeum • American Architecture Award
2008 • MIPIM/Architectural Review • MIPIM Future Project Award: Tall Buildings
2008 • MIPIM/Architectural Review • MIPIM Future Project Award: Overall
2007 • Miami Architectural Bienal • Bronze Unbuilt Project
List type, e.g. concrete or steel frame, wood, etc.: Concrete. Raft foundation supported on cast-in-place bored poles (foundation), reinforced concrete shear core wall (superstructure), reinforced concrete cast-in-place slab (floor system).
Manufacturer of any structural components unique to this project:
Concrete formwork: Peri, Munich, Germany
Structural precast: Index, Kuwait City, Kuwait
Piling: Edrasis Middle East, Kuwait City, Kuwait
The exterior wall consists of two basic types. The occupied office floors use a unitized glass façade for vision while the south-facing wall and structural spine of the tower is clad in a combination unitized limestone cladding and limestone trencadis.
Stone Makeup: 40mm Jura limestone, layer 10/11, sandblasted and brushed
Trencadis Makeup: 8mm Jura limestone, layer 10/11, brushed
Stone supplier: Jura Limestone Suppliers, Eichstat, Germany
Vision glass makeup: 6mm clear + PVB + 6mm Clear Guardian Sunguard Silver 20 #4 + 16mm Air Space + 6mm Clear Pilkington YBE0180 #5(second low-e coating only on flat glass panel).
Curtainwall fabricator: Wuhan Linghun Building Decoration Engineering, Wuhan, China
Glass supplier: Guardian Industries, Dudelange, Luxembourg
UNDERNEATH IT ALL
In tandem with the development of the scheme for the tower's superstructure, Sarkisian's team worked on the design of the foundation, starting with the assumption that the building would be around 70 stories tall and built of cast-in-place concrete. But as the tower concept took shape, it became evident that the spiraling form would concentrate gravity loads on the west side of the building footprint below the southwest flare wall, while very little load would be applied to the north and southeast edges. In response to this load differential, engineers devised a 13-foot-thick reinforced-concrete raft supported on 289 piles, each between 66 and 89 feet long, with the deeper piles located densely around the areas of greatest stress.
The roughly 200-by-230-foot raft, which required almost 30,000 cubic yards of concrete, was poured in 15 separate sections over a period of four months. This segmented approach was dictated largely by local production capacity, but it also helped contractors control the heat generated during concrete hydration—the chemical reaction that occurs when cement is mixed with water. If the material gets too hot—a particular concern given the desert environment—its strength can be compromised. Performing the work at night, along with the use of a concrete mix containing a high percentage of fly ash (a byproduct of coal combustion) also helped keep temperatures in check, says Ali Asfour, construction manager for Ahmadiah Contracting & Trading. The company is part of the client consortium and is the project's general contractor.
Construction of the beefy south-facing wall and the ribbonlike flare walls, which play an integral role in the building's lateral- and gravity-load-resisting systems, was also tricky. As part of a so-called “construction correction program” devised by SOM, the contractors adjusted the self-climbing formwork with each pour to compensate for displacement caused by the counterclockwise-torqued geometry. The process accounted for the elastic movement of the concrete under its own weight during construction and for long-term movement from shrinkage and creep. “Loaded concrete can hydrate for up to 10 years,” says Sarkisian, explaining the latter phenomenon. “Its properties can continue to change during that period,” he says.
Arguably, the tower's base presented an even tougher design and construction challenge than its sculpted superstructure. “How a supertall building meets the ground is always problematic,” says Aybars Asci, an SOM director. Compared to a lower-rise building, a supertall tower has a much smaller footprint relative to its height, but with many more people coming and going, he explains. It is also where gravity loads are greatest and where the structural elements tend to be the largest, he points out.
At Al Hamra, the architects created ground-floor space that could handle the tower's anticipated foot traffic by canting the perimeter columns on the building's north face, increasing the lobby's depth. Designers also made Al Hamra's nearly 80-foot-tall entry hall almost Gothic by devising a system of lamellae—a series of reinforced-concrete weblike vaults—that transfer the tower's gravity load to the foundations. Developed through nonlinear buckling analysis, the system works by reducing the unbraced length of the lobby columns and by decreasing the structural demand on each of them through load sharing with parallel members, explains Sarkisian. The lamellae's primary members are about 4 feet square where they meet the lobby floor. But without use of the bracing technique, the space would have required perimeter columns almost three times as large, he estimates.
The lamellae, which Asci describes as “structurally sensible but spatially interesting” were built with fiberglass formwork fabricated from shop drawings generated from SOM's 3-D model. Even so, constructing the lamellae was a slow process, requiring nearly 100 days to complete. In the meantime, work advanced on the rest of the tower, with floor framing on the north side catching up to the other sections of the building at the 52nd floor, according to Asfour.
White paint covers the lamellae, enhancing their filigree quality, but somewhat diminishing the brute power evident in construction photographs. “No one likes exposed concrete other than architects,” says Asci. Aesthetic concerns aside, however, exposed concrete was never a practical option, especially on the exterior, due to Kuwait City's salty gulf air and its tendency to corrode rebar. In part to prevent such deterioration, the architects chose an especially durable type of limestone cladding, covering the south-facing planar wall in 2.5-foot-by-4.5-foot panels. They clad the serpentine flare walls in the same stone, but with trencadis—a mosaic of shardlike pieces.
The treatment of the flare walls lends them a handcrafted character, especially evident up close. Their texture contrasts with the silvery smoothness of the insulated glazing units (IGUs) cladding the east, north, and west facades. The IGUs include a low-E coating that imparts just enough reflectivity to catch the sky, points out Haney. This coating proved to be one of the key curtain wall challenges, since the architects needed to make sure it would be compatible with the heating and bending process required to fabricate the glass that wraps the corners. These curved units make up 30 percent of the building's glazing.
The reflectivity that Haney is so fond of was evident on a sunny day in mid-March, even though the curtain wall was still covered with construction grime, as well as a coating of dust from the region's frequent sand storms. After an initial cleaning, the glazing will be cleaned once every three months by workers suspended from a maintenance unit that encircles the building on a track cleverly concealed within the steeply sloping parapet.